In a reciprocating piston internal combustion engine, there is usually provided for each combustion chamber a plurality of valves, the stems of which diverge in a direction away from the combustion chamber. When these valves are operated by a single overhead camshaft, rockers are required to transmit motion from the camshaft to free ends of the valve stems. One advantage of this arrangement is that the valves can have fairly large heads. This contributes to good flow of gases into and out of the combustion chamber.
In G.B. Pat. No. 2,005,347, there is disclosed on internal combustion engine with two valves per cylinder. The valves are driven by a single overhead camshaft and the axis of the camshaft is intersected by a longitudinal centreline of each valve stem so that no rockers are required. The cylinder axes are inclined to the horizontal and the camshaft axis is offset upwardly with respect to the cylinder axes. The centre of the head of one of the valves of each cylinder lies substantially in a plane containing the axes of several cylinders of the engine. The second valve is inclined to the first valve and the centre of its head is spaced from the plane containing the axes of the cylinders. The object of this arrangement is to enable the engine as a whole to be given a large inclination relative to the vertical, with a view to obtaining a power unit of low height.
In "Repair Operation Manual" for the Austin/Morris 2200 six cylinder engine, third edition published by British Leyland Limited, there is illustrated diagrammatically in FIG. 26 a pair of valve guides for valves associated with a common cylinder, these guides converging in a direction away from the cylinder so that the valves to be mounted therein can be operated by a single overhead camshaft.